Hormones are involved in a third of all cancers in the United States. Estrogens in particular have been implicated in cancers of the breast and of the female genital tract. Diethylstilbestrol (DES), a synthetic estrogen strongly linked to human cancer, can induce cancer in 100% of hamsters within six months. There is evidence to suggest that estrogens have a tumor promoting activity. In addition, estrogens may also participate in tumor initiation. Here, it is proposed to initiate a rigorous examination of the possibility that metabolites of estrogens can elevate background mutagenesis by one or more pathways. The following specific questions concerning the mutagenic potential of estrogens, using a reactive metabolite of DES as the model, will be addressed in this project. (1) Is diethylstilbestrol-4',4"-quinone (DES Q) mutagenic through a direct covalent or non-covalent interaction with DNA? (2) If it is mutagenic, (a) which DNA base is the most frequent mutational target? (b) what is the mutational specificity and which of the known genetic modulators of mutagenesis affect mutagenesis by DES Q? (c) does the mutagenic activity correlate with DNA damage at the level of nucleotide sequence? (3) If it is not mutagenic, does DNA damage occur without leading to significant mutagenic enhancement? The experimental strategy for detecting mutagenesis consists of in vitro adduction of model DNA genomes, their replication in Escherichia coli or in cultured human host cells, identification and sequence-level characterization of any mutations in marker genes. DNA damage by DES 0 will be assessed by covalent binding of radioactive estrogen to DNA, by the post-labeling method, by methods aimed at detecting cryptic damage, as well as by current molecular methods for mapping damage sites at the sequence level. Mutagenic potential of the non-covalent interactions DES Q with DNA will be assessed in an experimental system in which DNA will be replicated in vitro in the presence of DES Q, followed by transfection of the replicated DNA to evaluate mutagenic consequences.